Responding to a three-pronged attack: Desert lilies subject to herbivory by dorcas gazelles

We examined the effects of herbivory by the dorcas gazelle, Gazella dorcas, on different phenological stages of the lily Pancratium sickenbergeri from 1990-1996 in the Negev desert, Israel. We placed particular emphasis on the role of gazelle herbivory on selecting for plant defenses and the effectiveness of these defenses against subsequent herbivory. In the summer months, the gazelles dig in the sand to remove all or part of the bulb of the lily. Plants with partially-consumed bulbs were less likely to produce leaves the following winter and probably have lower lifetime flower production. Herbivory has resulted in greater downward growth of the bulb in populations with herbivory than those without herbivory, which reduces the probability that the entire plant will be consumed. Gazelles eat the leaves in the winter; this herbivory has a negative impact on leaf growth rates. However, the production of calcium oxalate limits gazelle consumption to the tips, and consequently reduces the effects of leaf herbivory. In the fall, the gazelles consumed virtually all flowers, yet we found no defence or growth strategy that might ameliorate this impact, with the possible exception of forgoing the output of a second flower stalk after the first has been consumed. The results of this study suggest that lilies employ different strategies to resist gazelle herbivory, and that these strategies are dependent on the phenological stage that is eaten. Avoidance by defence is the strategy in the leaves, avoidance by escape is utilized in bulbs. Forgoing the output of a second flower stalk after the first has been consumed can be considered as a form of escape based on a bet-hedging strategy or a shift in energy allocation.